1. Field of the Invention
This invention relates to vacuum cleaners and the like and, in particular, to wheeled support structures for use therein.
2. Description of the Background Art
It is conventional in vacuum cleaner apparatus to provide wheeled support structures permitting movement of the vacuum cleaner apparatus over the floor surface to be cleaned. In one form of vacuum cleaner apparatus, the suction means is provided in a wheeled canister and suction is applied therefrom through a flexible hose connected to a wheeled nozzle adapted to be moved over the surface of the floor. To facilitate manufacture and minimize cost, it has been conventional to utilize snap-on fastening wheels, such as providing the wheeled mount of the canister body. It has been conventional to form such wheels of a relatively high modulus, stiff material, such as ABS synthetic resin (acrylonitrile-butadienestyrene).
Such relatively hard wheel material is satisfactory for use on vacuum cleaners which are moved to-and-fro over carpeted floors only. However, when the vacuum cleaner is used for bare floor cleaning as well as carpet cleaning, as is usually the case, it is desirable to form the wheels out of a relatively soft, low elastic modulus material, i.e. one having relatively low stiffness so as to avoid scratching of the bare floor surfaces by the wheels. However, heretofore wheels made from such relatively soft low elastic modulus synthetic resins such as polypropylene did not have the desired strength and other physical characteristics to permit use thereof in a snap-fitted wheeled structure.
One example of a caster formed of synthetic resin is that illustrated in U.S. Pat. No. 3,928,888 of Sidney D. Lapham. As shown therein, the support disc is provided with a tapered bearing element which supports a portion of the weight of the element carried thereby. Additionally, an annular bearing surface is provided for further supporting the load. The periphery of the disc is further supported by a wheel rotatable about a horizontal axis.
In U.S. Pat. No. 3,991,434 of Michael J. James, a ball caster is provided wherein an axle is provided on the body structure, with the wheel defining a female hub element rotatably journaled on the body axle.
In U.S. Pat. No. 1,338,356, of John S. Cantelo, there is shown a caster having the load-bearing support of the wheel at the axle, with clearance between portions of the wheel radially outwardly thereof and the supporting body.